Process of producing electrolytic foraminous sheets



E. o. NoRRls 2,226,381

PROCESS OF PRODUGING ELECTROLYTIC FORAMINOUS SHEETS Dec. 24, 1940.

Filed April 22, 1938 y Patented beez-1,1940

' UNITED STATES PATENT OFFICEvv rnocsss or rnonUcmG mcraom'rlo rorummous sul-:ars

AEdward .-NorrlI.`Westport, Conn., assigner to Edward 0. Norris, Ine.. New York, N. Y., a oorporation o! New York Application April z2, lass, serial No. 203,503 s calms. l(ci zur-11) a process for reinforcing existingforaminous sheet.

In my copending application Ser. No. 52,334, led November 30, 1935, I describe a process of making a sheet metal screen `by electro-deposition of metal on ak metallic matrix formed with inserts of electric insulation, such inserts lying substantially flush with the surface of the matrix on which the. metal is to be deposited. The inserts serve to form gaps or apertures in the metal deposited on said surface, but as the electro-deposition proceeds it gradually builds out over the insulated areas choking the apertures, and if continued will eventually result in complete closure of the apertures. Thus, for any given spacing and size of apertures there is a definite limit to the thickness of metal that may be deposited. Because of this limitation the resultant screen may be too frail and iiimsy for practical use, particularly in the case of fine mesh screens having apertures of microscopic dimensions.

It is an object :if the present invention to provide a process which will `overcome this limitation, so that a fine mesh sheet may be produced of much heavier cross-section. It is also within the purview of my invention to reinforce an existing fine mesh sheet by thickening it and yet preserving in the finished product a predetermined size and si acing o-f apertures.

A novel feature of myl invention consists in the employment of a novel method of etching which will attack chiefly the metal bounding the apertures. Thus, a greater thickness 'of metal may be deposited on the matrix, the electro-deposition being before the apertures are closed over, and then my novel etching method serves virtually to ream out the apertures until-they are of desired size.

It is also within the purview of my invention to form a thinv sheet in accordance with the process set forth in said copending application and then to reinforce said sheet by electrodeposltion of metal which is halted before the apertures of the sheet are closed, and finally etching out the apertures to predetermined gauge.

Other objects and advantages of my invention will appear in the following description of a preferred process and la modiilcation thereof, and

thereafter the novelty and scope of the invention will be set forth in the claims.

In describing my method, I will do so in connection with the production of what is ,ordinarily known-as "screen such as is used for ltering liquids, segregating materials, excluding'insects from enclosures, photoengraving, dial prov duction, and the like.

In the accompanying drawing:

Fig. 1 shows in perspective a portion of a 10 screen electro-deposited upon amatrix;

Fig. 2 is a view in crosssection of the screen showing a deposit of reinforcing metal thereon;

Fig. 3 is a view in cross-section of apparatus with which the apertures in the reinforced screen 15 are etched 'out to desired gauge; and

Fig. 4 is a view similar to Fig. 1, showing a modification of my process in which the screen is biilt up to its final thickness in a single plating s ep.

The matrix shown in Fig. 1 may be formed as described in said copending application. It comprises a plate of metal l0 having a surface formed with pits ii which are f'dled with electric insulation, as indicated at I2. .It will be observed 25 that the matrix has a fiat upper surface, since the inserts I2 lie flush with the metal of this surface.

The matrix is prepared for plating in accordance with common practice, by insulating all but 30 the surface thereof which is dotted with the in# serts I2, and this surface, on which metal is to be deposited electrolytically, is waxed or otherwise treated to facilitate stripping o-ff the deposited metal therefrom. The matrix thus prepared is placed in an electro-plating bath, forming the cathode thereof, and a layer of metal il is then electro-deposited on the matrix. This metal builds up on the exposed metallic surfaces surrounding the inserts I2, forming a network of bars with apertures l5 therebetween at 40 Ethe insulated areas i2. As the electro-deposition proceeds the deposit will gradually grow over the areas i2, as shown in Fig. 1.

In my preferred process the electrolytic action is arrested before there is a material overlap of metal on the areas l2. The thin sheet of apertured metal il is now stripped from the matrix and is placed in the same or another electroplating bath to receive a further metallic deposit. Since the screen is not backed by the matrix, metal will be deposited on b'oth faces thereof. The appearance of the screen with its coating i6 supplied by the second plating step, is shown in cross-section in Fig. 2. Preferably the original resistance to certain etching fluids that will readily attack the reinforcement metal I6. Thus, the original deposit Il maybe formed of nickel and the layer I8 electro-deposited on the nickel may be of copper. However, such thickening or reinforcing. of the original deposit causes a material reduction in diameter of the apertures I5, and accordingly the next step consists in enlarging these apertures.

I have found that when an etching fluid is poured thru the screen it will attack the metal bounding the apertures much more actively than that of the intervening areas. This effect, I believe, is due to a comparatively static condition of the etching iiuid on the upper faces of the screen between the apertures, and obviously the underside of the screen will be less exposed to the etching fluid, because the latter passes by gravity directly through the apertures and wets the inside of the screen only indirectly as a result of surface tension of the etching fluid. In my opinion the comparatively quiescent etching fluid on the lands of the screen forms a substantially sated film that serves to protect said lands from attack by the more active etching iiuid, while in the apertures such protecting film is carried away as fast is it forms, so that the walls of the apertures are constantly exposed to fresh highly active etching fluid. Forinstance, if the metal is copper and the etching uid ferric-chloride, the fluid in immediate contact with the metal will form cuprous-chloride which will remain as a thin protective film on the lands but will be Washed off the aperture walls. Whether l this theory of operation be correct or not, I have found that by this step of the process the apertures of the screen may be very readily enlarged without appreciably reducing the thickness of the screen.

In Fig. 3, I show an apparatus which may conveniently be used to etch out the apertures. This comprises a vat provided with drain pipe 2|. Etching fluid is introduced into the vat 20 through an inlet pipe 22. The pipe 22 discharges etching fluid into a hopper 24 which is formed at the bottom with a marginal lip 25 on which the screen to be etched may be supported. The fluid accumulates to a suitable level 26 in the hopper and pours through the apertures Iinto the vat 20. Means (not shown) may be provided for pumping the discharge from pipe 2I to the inlet 22. The etching'i'luid attacks the metal forming the walls of the apertures I5 to a much higher degree than it does the intervening surface metal and in this Way the apertures may be enlarged from the size indicated by broken lines in Fig. 3

to a predetermined size such as thatindicated by full lines in the same gure, Without appreciably reducing the thickness of the screen. For lnstance, ferric chloride may be used as the etching fluid, since it has the property of corrosive action on both the copper and the nickel. An alternative is to employ an etching fluid which selectively reacts on the copper to the exclusion of the nickel. An example of such an etching fluid is a solution of chromic acid and sulphuric acid in water in about the following proportions by weight:

Per cent Sulphuric acid 16 Chromic acid 8 Water '76 As a modification 'of the process described above, it will be evident that the electro-deposideposit I4 is of a metal which will oier high,

tion of metal on the matrix may be accomplished in-a single step. In other words, on the original matrix I0 a suitable metal may be deposited until the apertures I5 are nearly closed. as shown in Fig. 4, thus building up a much thicker sheet than has heretofore been possible for a given mesh. This thick sheet of metal is then treated in the manner illustrated in Fig. 3 to etch out the apertures to the desired size, as indicated by broken lines in Fig. 4. Obviously, in this modified process it will not be possible to obtain so thick a screen as in the preferred process, because the metal is deposited on one face only. However.- the process may be used where the desired thickness of the finished screen is only slightly greater than that possible for a given mesh without etching out the apertures. Manifestly, the screen produced by either process may be built up to any desired thickness by repeatedly electro-depositing metal thereon and etching out the screen apertures after each deposition oi' metal.

It-will thus be observed that my invention is capable of certain modifications and consequently the preferred process and the modification thereof set forth above are to be taken as illustrative and not limitative of my invention, and it will be understood that I reserve the right to make various changes therein without departing from the spirit and scope of my invention as set' forth in the following claims.

I claim:

1. A method of producing a ne mesh screen, which comprises the steps of electro-depositing metal upon the screen, arresting such electrodeposition before the screen apertures are closed over by the deposited metal, and etching out the apertures to predetermined size by maintaining a head of etching liquid upon the screen and causing the liquid to flow through said apertures.

2. The method of forming a fine mesh screen which comprises the steps of electro-depositing metal on a metallic matrix dotted with resist areas, continuing suchdeposit until the apertures in the deposited sheet at the resist areas are almost closed, stripping the deposited sheet from the matrix, and etching out the apertures to desired-size by maintaining a predetermined head of etching liquid on said sheet and causing the Aliquid to stream through said apertures.

3. '/I'he method of forming a ne mesh screen which comprises the steps of electro-depositing metal on a metallic matrix dotted with resist areas, arresting the electro-deposition of metal before the apertures in the deposited sheet at the resist areas have been materially reduced, stripping the deposited sheet from the matrix, electro-depositing metal on both surfaces of the deposited sheet, arresting such deposition before the apertures in the sheet have been closed over, and etching out the apertures to desired size by maintaining a head of etching liquid on said sheet and causing the liquid to stream through said apertures.

4. A method of forming a fine mesh screen,

which comprises the steps of electro-depositing metalv on a metallic matrix dotted with resist areas, arresting the electro-deposition of metal before the apertures in the deposited sheet at the resist areas have been materially reduced, stripamasar i A 3 uid on the coated sheet and causing the liquid to vstream through the apertures therein, the metal o! the original deposit being of such nature as to offer a higher resistance to said etching liquid than does coating metal.

5. A method of forming a tine mesh screen, which comprises the steps of electro-depositing metal on a metallic matrix dotted with resist areas, arresting the electro-deposition of metal before the apertures in the deposited sheet at the resist areas have been materially reduced, stripping the deposited sheet from the matrix. electro- 

